Ants & Aphids

I was taking closeups of flowers with my macro lens when I saw a few ants going up and down the stems of 2 daisies. It wasn't apparent what they were until I could open my photos on my computer, when I could see the ants were herding some aphids. I've heard of it, but never seen it before. Ants are able to extract a sweet clear liquid from them. Aphids go through various stages of development. This is one of the earlier stages, eventually ending up as a tiny soft green insect with wings.